The Luther Building and Albert J. and Judith A. Dunlap Cancer Center is a new 5-story, 358,000 square foot hospital addition that includes a comprehensive Cancer Center, Family Birthing Center, and outpatient Surgery Center as well as increased space for inpatient care beds. The building overlooks the beautiful Half-Moon Lake in Eau Claire, Wisconsin, and is part of the Mayo Health System. The facility was composed of: two, five-story towers plus a basement; a single-story cancer center plus a basement; a five-story, 183-foot long skywalk; a one-story raised single level 70-foot long skywalk; a two-story concrete connector; a 250-seat tiered auditorium, and a 10,000-square-foot, single-story radiology addition. The project’s concrete mix designs were specially formulated to optimize the long term durability and field performance, while reducing the carbon footprint through using local material and recycled flyash.

The state-of-the-art cancer center includes two linear accelerators with rooms that have four- to eight-foot thick concrete shielding walls. Both skywalks incorporate concrete mat pile foundations with micro-piles to support the lateral resisting frames that were as close as two feet from an existing basement wall. The auditorium is located in the basement of the south five-story bed tower and has three 60-foot long steel transfer beams incased in concrete for aesthetics, fire-resistance, and continuity. The fifth floor was built as a shell space available for future growth.

A conventional 12-inch concrete flat slab structural system was chosen for its shallow structural system depth that allows uninterrupted space for the large amount of mechanical and plumbing required in healthcare facilities. Concrete’s natural superior vibration control with its large floor mass and monolithic construction is ideal for use in the operating rooms and other areas with sensitive equipment or resting patients. The flat slab system also allowed highly flexible column grids with a typical 32–by-22-feet bay size to create efficient floor layouts and a beautifully curved precast concrete panel façade while limiting the height of the building and cost of the facade. The thin system allowed an economical solution to blend the height of the new construction with that of multiple eras of the hospital’s buildings dating back over 100 years. The third floor of the north tower also integrated concrete transfer beams to recess the exterior wall of the top floors.

The lateral system for the main towers and cancer center used 10-inch thick concrete shear walls around the three elevator shafts and three stair shafts. The building is supported on concrete spread footing foundations and mat foundations under the shaft walls. The basement housed many of the heating, ventilation and air-conditioning (HVAC) systems and required a 21-foot floor to floor distance which resulted in 24-inch thick concrete foundation walls on approximately 50 percent of the building perimeter. In addition, two large area wells were designed to allow the replacement of large mechanical equipment without disruption to the site or building occupants.

The flexibility of the architectural layout and mechanical, electrical, and plumbing revisions during construction combined with the inherent fire resistance and durability made a concrete two-way flat plate system the most economical and appropriate structural system.